In 2011, the aviary population of non-releasable songbirds exhibited over the previous 15 years had been reduced to one Mourning Dove. Sensing an opportunity, I made a proposal to the staff with my idea to answer some Blue Jay questions. With no opposition, I proceeded to plan the project. The project had three goals:
- Give visitors an opportunity to observe Blue Jays up close.
- Include an accompanying exhibit on Citizen Science.
- Conduct research to determine if social hierarchy in Blue Jays affects their use of novel foods.
In April of each year volunteers were trained and 10 Blue Jays were captured in funnel traps. At capture the Blue Jays were aged, weighed, and measured. Blue Jays can be aged as either first year birds or after first year (adult) by looking at the markings on the outer wing coverts (small feathers overlapping the primary flight feathers). Half the Jays captured were first year and half were adults. We were unable to determine the sex of the birds since male and female Blue Jays are not dimorphic in their plumage and they were not in breeding condition at the time of capture. Before releasing the jays into the aviary each bird was color banded. The color bands consisted of two colored plastic bands placed on the right leg of each bird. The different combinations of color bands allowed us to identify each bird. Once in the aviary the birds had time to acclimate to their new surroundings. Observation periods began on May 1.
The project had two phases. The first phase was to determine which Blue Jays were dominant and which were more submissive. This was determined by which bird displaced another at a feeder that contained a commercial songbird seed mix and pelletized commercial captive bird diet. After two months of observations the hierarchy was established and the second phase began. Over the three years of the project, the first phase covered a total of 162 days with 13,988 observations.
The second phase focused on determining the order in which the Blue Jays arrived at the feeder and how often they utilized a novel food. A novel food was introduced during each observation period on one feeder, with the second feeder containing the regular diet. A coin flip determined which feeder received the regular diet or novel food. Fifty novel foods were used each year, including different sizes, shapes, and colors of dyed cooked pasta, large parrot pellets of different colors and shapes, tropical nuts and fruits cut into various shapes and sizes, strips of raw fish, ground horse meat rolled into small logs, a variety of breakfast cereals, snack crackers, and pet kibble. Over the three years of the project, the second phase covered 140 days with 3,062 observations.
In the second phase there was very little interaction between jays at the novel food feeder. Most novel foods were larger in size than the regular basic diet offering, and as a result were usually picked up and taken to another perch before being eaten. There was little aggressive behavior displayed at the feeder, but after flying to a perch, occasionally one bird would attempt to steal the novel food from another one that had acquired it. Novel food was also occasionally cached (stored) and another jay would recover the food item, but the identity of the “pirate” stealing the cached food was seldom determined. The use of novel foods varied widely. Generally, smaller sizes of novel foods were preferred over larger sizes. Surprisingly, the color of novel foods did not seem to be a factor, but texture was. Novel foods that were slippery or sticky (dried fruits, banana slivers, marshmallows) were picked up but rejected more often than they were eaten. During both phases, the Blue Jays were observed capturing insects that had flown or crawled into the aviary. Several species of bees and moths were taken while flying. Caterpillars of unknown species were picked off the aviary mesh and larva of the Viburnum leaf beetle were gleaned from the leaves of an Arrowwood shrub.
Weather data was not recorded, but overall activity was greatly reduced during periods of rain as the birds tended to stay under shelter. Another factor that reduced activity was the presence of predators outside the aviary. Cooper’s Hawks were a particular concern of the Blue Jays. On nine occasions when a Cooper’s Hawk perched outside the aviary, the jays showed one of two behaviors. Most jays would remain quiet and perfectly still, while one or two would sound the familiar “jay, jay, jay” alarm call. Within seconds of the intruding hawk’s departure, activity would resume. Unfortunately, the identity of the vocalizing jay(s) could not be determined.
What did we learn? After all the data were compiled and analyzed, the results showed the following:
- There was little size difference between the most dominant birds versus the most submissive birds based on weight and length of wing chord (wrist to longest flight feather).
- Adult birds were twice as likely to be dominant as younger birds.
- Dominant birds were slightly more likely to feed with other birds than feeding alone.
- The submissive birds were slightly more likely to feed alone than with other birds.
- There was no significant difference between the most dominant and least dominant in their total use of novel food, but dominant birds were nearly four times more likely to be the first to investigate a novel food.
Another question came up was whether Blue Jay populations are affected by Gray Squirrel population levels. This question resulted from the number of hours it took to capture the Blue Jays before each year’s study period. Over the three years of the study, the number of hours it took to capture the Blue Jays increased exponentially each year as the number of Gray Squirrels near the capture sites increased. Blue Jays and Gray Squirrels do compete for some foods, including mast like acorns. It is possible that Gray Squirrels out-compete Blue Jays for important food resources. Other studies have also noted that during periods of higher squirrel densities, squirrels can be important nest predators on many bird species, including Blue Jays.
Clearly, there is no limit to the number of questions that can be pondered when we consider the complexity of the natural world. For my part, I want to thank the Science Center for allowing me to try to answer one small question that I had often wondered about. I also want to thank the terrific volunteers who gave so many hours to the project. Without their help, I could never have pursued the answers to my question.